1. Field of the Invention
The present invention relates generally to a damper for supporting a power unit (combination of engine and transmission) and more particularly to a damper arrangement which attenuates roll vibration using viscous shearing resistance.
2. Description of the Prior Art
JP-A-63-14036 discloses a damping arrangement wherein a circular plate or disc is mounted on a shaft or similar member which is rigidly connected with the power unit. The plate is disposed in a circular housing or casing in a manner to be immersed in a viscous fluid. The casing is connected to the vehicle chassis by way of a linkage which induced relative rotation between circular disc and the circular housing.
However, this arrangement has suffered from the drawback that the power unit is supported on the chassis by elastomeric members in a manner to be simultaneously movable in a plurality of directions, the power unit does not just move in the role direction but tends to move randomly in different directions in addition to the roll one. Accordingly, the actual device is required to include a linkage which has:
1. a connecting member which is made of flexible plate and which acts a spring link; or
2. at least one elastomeric bush between the casing and the chassis; or
3. a combination of a flexible link and elastomeric bushes.
In the case a spring link is used, while the spring link is subject to tractive forces, there is no problem, however, when the link is subject to compressive forces, the link tends to flex and thus reduce the relative rotation between the housing and the disc. This of course reduces the effectiveness of the damper.
In the case wherein one or more elastomeric bushes are used, when rolling motion of the engine occurs, the bushes distort in a manner which reduces the amount of relative rotation which is produced between the disc and the housing and thus again the damper is not used to its full potential.
A combination of elastomeric bushes and a flexible connector only increases the problem and markedly reduces the amount of relative rotation which is induced.